1. Field of the Invention
The invention relates to a system for measuring the surface topography of a lapping plate, and for analyzing and presenting the data resulting from such measurements.
2. Background Information
Lapping plates are often used in the process of manufacturing semiconductor devices to accurately remove excess material from device surfaces. FIG. 1 shows a typical application in which the air bearing surface 11a of a strip of thin-film magnetic heads 11, which are being manufactured for use in hard disk drives, is being lapped to set the height of the heads' magnetic sensors within specified limits. The lapping plate 12, rotating at constant speed and impregnated with fine abrasive particles, mechanically removes material from surface 11a at a controlled rate. A holding device (not shown) precisely maintains the position of the magnetic heads 11 in contact with the lapping plate 12 during the lapping process.
A lapping plate that would be used in manufacturing thin-film magnetic heads is typically made with an aluminum base to which a layer of a tin alloy is bonded. The surface of the tin alloy is then machined (“planerized”) to achieve a flat, smooth surface. Prior to use, the tin alloy face of the lapping plate is impregnated (“charged”) with fine abrasive particles, typically diamond dust. The charging process is accomplished by rotating the lapping plate while dripping a liquid slurry of the abrasive particles onto the surface of the tin layer and pressing in the particles with a charging ring.
The quality of a component surface being lapped is affected by the presence or absence of irregularities in the surface of the lapping plate. Such irregularities can, for example, cause scratches in the air-bearing surface of a magnetic head that will result in aerodynamic instability as the head “flies” over the surface of a hard disk and consequently, result in unreliable read/write operation of the hard disk memory.
In order to measure the surface topology of a lapping plate and determine its suitability for use, the lapping plate is placed in a measurement apparatus that typically has a spindle for rotating the lapping plate, and a linear actuator for moving a probe radially across its surface. The probe is able to obtain samples of the surface height at different distances from the center of the plate, and at different angular positions of the plate. Because of the degree of precision required in positioning the probe, the measuring apparatus may be quite expensive. Typically, the data obtained from these measurements must be processed off-line in order to obtain the surface characteristics. These methods do not automatically yield a characterization of the lapping plate surface in terms of a set of parameters that can be used in gauging the quality of products that will be produced using the lapping plate, and hence, are not capable of readily generating a simple pass/fail determination for the operator making the measurements.